This thesis describes laboratory measurements of the O2 A-band spectrum using frequency stabilized cavity ring-down spectroscopy (FS-CRDS). The FS-CRDS allowed the collection of high-resolution (<1 MHz) spectra in conjunction with the exception sensitivity of the CRDS technique. Line positions were measured with an accuracy better than 2 x 10 -5 cm -1 by calibrating our spectra against the hyperfine components of 39K D lines. Line parameters were determined using a variety of lineshape models from the standard Voigt profile to models incorporating speed dependence and collisional narrowing. Clear deviations are shown between the observed and Voigt profiles, while the other profiles considered were found to fit the observed lineshapes well. Line intensities obtained using the Galatry profile are compared with previously measured values and found to be approximately 1% smaller than intensities found in current databases. Many of the other lineshape parameters are in good agreement with previous measurements. However, the pressure-induced shifts of the current work are considered much more accurate than other studies. Finally we report on the line parameters of each of the isotopologues of O2.